Microgreens with LED strips?

[Deece]

Hi all!

I purchased some gear to build a 2x4' light using 22" bridgelux strips. I can run it at 240W at 1A but I can ramp it down to half that, 120W at 500mA.

My original intent was for a grow tent for marijuana but II'm thinking about separating it into 4 small lights each with 3 strips and hang on a storage shelf and grow microgreens with.

The light temp is 3500K, does anyone have any experience growing microgreens with led strips? Think this light temp will hold me back? research suggests 6500K is standard for microgreens.

Also, if the lights are at about 12" height is 120W going to be an ok intensity for the microgreens? Assuming 2sqft per shelf this would add up to 8sqft total, so I could ramp the driver from anywhere between 13W/sqft to 30W/sqft.

I can still obviously hang them all in series if i do want to use them in teh grow tent.

Thoughts? I'll probably do an experiment with the microgreens, and pit the led strips against a t5HO fixture (running I think 5000K) and a mars reflector 96 blurple led. Who has interest in seeing this experiement go down?
cheers!
Deece

[ATPinMotion]

We have used 3500k EB gen 2's with really good success. I don't think the CCT will hold you back.

120w in 8sq ft is WAY more light than microgreens need. We have found 5-10watts per square foot to be optimal for microgreens and lettuces when the lights are hung at 8"-12".

I would suggest hanging your fixture at 2' to start with.

[unkle_psycho]

If I planned to use led to grow microgreens I would look at the 12/40w TRP drivers starting around 5-6$ on digikey. You only need a tiny bit of light for two days on microgreens right?

[The_Mouse_Police]

More than two days. Anywhere from about 5 to 21 days. But, most microgreens are happy with 100 uMols/s/m^2, or around 700 lux, and some even lower than that. Even "hungry" ones, like basils, max out below 250 uMols, and grow alright with less. Coverage is more of a concern than photons. The closer the strips are to the plants, the more strips you'll need, to reach all the leaves.

Compared to typical setups for MJ, divide by 8, and you'll be the right ballpark.

6500K is probably for fluorescent tubes. You can't directly compare CCT if different lighting tech.

[unkle_psycho]

I was playing around on paper with diode distances, imagining that the spreadsheet images of light distribution, and the diode angle 120deg held true.

I drew lines out of a imaginary diode at 120deg and looked at what distance they converged... I started feeling I should design something like QB's for salad, with an even coveradge, and I think I calculated one diode per 4cm in all directions.

I should probably order an empty QB and make one as a prototype.

I was thinking it would result in cheaper modules, and the ability to run really close at really low power levels.

[The_Mouse_Police]

If you can get PCBs cheap enough, it probably would. Bigger PCBs being expensive is what makes the strips such a good value. OTOH, as low as the power is, custom microgreen/seedling strips could be pretty thin.

[Deece]

Thanks guys!
One reason I suggest 2sqft per row is the fact the strips are 22" long. The shelf however is 36"x18" deep. Would it be fine to run three 10"x20" trays? It would mean 22" of light to cover a length of 30". This would be about 3sqft per shelf or 12sqft total.
As for depth I figure 2 strips to cover the 20" width... But could it be possible to run one strip per shelf..? I.e. could the strip cover a width of 20"? I don't have a great understanding of the 120deg viewing angle and/or how to calculate coverage given distance to light.

[The_Mouse_Police]

One could, but two would be better, as a minimum. With two of them, all the leaves get at least two angles to receive light from, and with them spread out, you won't be feeding the center ones an overabundance of radiation.

[unkle_psycho]

If you can get PCBs cheap enough, it probably would. Bigger PCBs being expensive is what makes the strips such a good value. OTOH, as low as the power is, custom microgreen/seedling strips could be pretty thin.

I'd love to know anything possible about how PCB size affects price, to allow the whole idea to keep maturing in the back of my mind. I see a lot of super cheap products with rather large PCB's so I was imagining they could be cheap.

The 4cm distance is something I calculated that I wanted to try, kinda because I thought it would preform well. I still think it would take a shit load of diodes per m2, so as a financial calculation it would probably be better to go for 6cm and maybe half the diodes. Anyway I would like to do a series of tests at similar power levels, but different distances and diode placements, just to see for myself how much difference it would make.

[The_Mouse_Police]

In absolute terms, Chinesium may work wonders, in quantity.

In relative terms, PCBs are printed circuit boards, and go through a multiple stage printing process (a few stages are usually done with specialized inkjets), and are then cut down to final boards. Whether aluminum backed, solid plastic, or fiberglass (most common), manufacturers make a single big panel, print it, drill it, plate it, and cut it (assuming 1-2 layer only). The costs are approximately the same for any panel with the same materials and coatings, regardless of how many final boards it makes. So, the more that can be cut from one panel, the cheaper each board can be.